Abstract

The aim of the project was to investigate the behavioural and
physiological strategies used by wigeon to maximise their
nutrient intake during winter. The reasons for selecting this
species were its totally herbivorous diet, its simple digestive
physiology and its small body size, all of which should lead to
problems in gaining sufficient nutrition during the winter.
The daily energy expenditure of this species was estimated from
faecal output studies to be 150 kcal bird-1 day-1. This figure
was compared with estimates for the larger grazing geese in order
to assess the effect of body size on energy intake. The strategy
of feeding for long periods (as much as 17 hours per day) to
increase food intake seems to be very important in this species.
Feeding site selection was investigated as this is an obvious way
to increase nutrient intake. Wigeon show clear preference for
particular feeding sites both in terms of amount and timing of
use. Grass biomass, grass protein content and proximity to water
are all important factors in site selection, reflecting the
requirements for efficient feeding and safety from predators.
Fertilization of a site increased its use by a factor of 2.5 A
spectrophotometer for grass biomass assessment was designed and
built for this part of the work.
The behavioural changes resulting from differences in grassland
type were studied. An increased biomass (and protein content) of
grass on a site resulted in higher peck rates, slower walking
rates and increased defaecation rates. These changes increased
the efficiency of food intake on high biomass areas and allowed
birds to exploit optimally a patchy food resource. The effect of
grass height on peck rate was also investigated.
Wigeon grazing has a great effect on the biomass, height and
spring production of grass on their feeding sites. Of more
importance is the fact that winter grazing can signficantly
affect the protein content of grass in the spring. This effect
is caused by the increased turnover rate of leaf material on
grazed sites.
The pressures leading to the tight feeding flocks, characteristic
of this species, were studied. The flock-feeding strategy is
likely to be important for nutrient intake since it leads to an
increased protein intake in spring, and may also allow
information regarding good feeding sites to be exchanged.
Studies on vigilance activity showed that a decrease in vigilance
time is important in small flock formation. This would have
advantages for both feeding efficiency and safety from predators.
The reduced likelihood of individual predation is also important
in producing larger flocks.
Finally, the physiology of wigeon digestion was studied. Wigeon
have a very rapid throughput time and a low digestive efficiency.
The storage of protein in the form of gut -tissue may also be important for breeding reserves in female birds.